Numerous steam assisted recovery processes are known for recovering bitumen from underground formation including Cyclic Steam Stimulation (CSS) and Steam Assisted Gravity Drainage (SAGD). Essentially, these steam-related processes involve the application of steam (i.e. heat) to a hydrocarbon-containing reservoir to reduce the viscosity of oil and/or bitumen therein and enhance its ability to flow. For example, during SAGD operations, steam introduced into a reservoir through a horizontal injector well transfers heat to the heavy oil upon condensation. The heavy oil with reduced viscosity due to this heating drains together with steam condensate and is recovered via a producer well disposed parallel and beneath the injector well.
Various techniques can provide for steam generation but the costs related to steam generation can often limit the economic feasibility of such techniques. Given the quantity of steam required for many of these steam-related processes, energy needed to generate the necessary heat for the steam generation represents a substantial cost. In addition, the associated environmental costs, including generation of greenhouse gases, can present severe limitations. In particular, the production of CO2 emissions that contribute to greenhouse gas as well consumption of fresh water for the steam generation are parameters in existing steam generation techniques that need to be reduced to the maximum extent possible.
Direct combustion steam generation may facilitate lowering these costs due to improvements in efficiency, inherent makeup water replacement, and reduced emissions. Direct steam generation operates by burning a fuel in a combustor and preferably injecting water into the combustor to produce a mixture of generated steam and the combustion products from the steam generator for injection into a hydrocarbon-containing reservoir.
U.S. Pat. No. 8,353,342 describes a direct steam generation method and apparatus that includes both generating steam for injection into a wellbore and capturing CO2 produced during steam generation in order to control CO2 emissions. Specifically, a method of steam assisted recovery of oil is described that includes first reforming natural gas to produce CO2 and hydrogen, followed by separating the CO2 from the hydrogen. Oxygen is also separated from other air components. Steam is then generated by introducing the separated hydrogen and oxygen into a combustion area where the hydrogen and the oxygen are ignited then contacted with water in the combustion area. The steam that is produced is injected into an injection well and includes products from combustion of the hydrogen and the oxygen as well as the water vaporized by heat from the combustion. According to the described method, therefore, produced CO2 is captured by sequestering the CO2 independent of injecting the steam into the injection well.
More recently, the benefit of co-injecting the produced CO2 with steam in direct steam generation techniques for oil recovery has been considered. In particular, the combustion gases, including CO2 which may be miscible in the oil and further serve to reduce its viscosity by swelling of the oil through gas solubility, introduce additional recovery mechanisms to the viscosity reduction associated with the injection of steam alone. Still further additional recovery mechanisms include: increased reservoir pressure, and movement of oil via reduced viscous drag. Furthermore, the injection of combustion gases downhole can address the emissions issues that arise with conventional surface steam generators.
Importantly, however, while co-injecting CO2 with steam may benefit steam-assisted oil recovery operations by lowering the steam to oil ratio, for example, the desired concentrations of the CO2 within the steam to achieve such benefits for any particular steam-related oil production process may not, however, coincide with output from the direct steam generation.
International Patent Publication No. WO2007/081816 describes a direct combustion steam generator in which water is introduced into a vortex sustaining container and flows through the container in a spiraling manner to create a liquid vortex. The swirling water surrounds the flame and combustion is carried out inside the rotating body of water. The combustion product is achieved by supplying fuel and tangentially supplying an oxygen containing gas to a burner to produce the flame. Combustion is carried out using air enriched with oxygen at varying concentrations (or even pure oxygen) in order to provide a vapor stream consisting of steam and the desired level of CO2. The hydrocyclone design of the generator is described as being capable of withstanding the flame temperatures encountered with combustion of fuel with oxygen or enriched air.
United States Patent Publication No. 2014/0060825 discloses the ability to control CO2 levels in the output mixture of steam and CO2, by controlling the temperature of the water fed to the steam generator. Specifically, a method of generating a mixture of steam and CO2 is described as including supplying fuel and oxygen into a direct steam generator in addition to water that is heated to above 200° C. Combusting the fuel and oxygen in the direct steam generator as the preheated water is introduced, produces a mixture of steam and combustion products that has a CO2 level in mass percent of steam below 11 percent.
A need continues to exist in the oil recovery industry for improved methods and systems for generating steam and non-condensable gases, such as CO2 mixtures, for best optimized recovery of heavy oil and bitumens from hydrocarbon-containing reservoirs which allows for optimal (and continuous) control of CO2, steam, and nitrogen by a reservoir engineer when same injected downhole to best produce oil from a particular well within a unique formation of specific viscosity, ambient temperature, porosity, permeability, and pressure, over time.
The above background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.